std::try_lock
From cppreference.com
Defined in header <mutex> | ||
template<class Lockable1, class Lockable2, class... LockableN> int try_lock( Lockable1& lock1, Lockable2& lock2, LockableN&... lockn); | (since C++11) | |
Tries to lock each of the given Lockable objects lock1, lock2, ..., lockn by calling try_lock in order beginning with the first.
If a call to try_lock fails, no further call to try_lock is performed, unlock is called for any locked objects and a 0-based index of the object that failed to lock is returned.
If a call to try_lock results in an exception, unlock is called for any locked objects before rethrowing.
Contents |
[edit]Parameters
| lock1, lock2, ..., lockn | - | the Lockable objects to lock |
[edit]Return value
-1 on success, or 0-based index value of the object that failed to lock.
[edit]Example
The following example uses std::try_lock to periodically tally and reset counters running in separate threads.
Run this code
#include <chrono>#include <functional>#include <iostream>#include <mutex>#include <thread>#include <vector> int main(){int foo_count =0;std::mutex foo_count_mutex;int bar_count =0;std::mutex bar_count_mutex;int overall_count =0;bool done =false;std::mutex done_mutex; auto increment =[](int& counter, std::mutex& m, constchar* desc){for(int i =0; i <10;++i){std::unique_lock<std::mutex> lock(m);++counter;std::cout<< desc <<": "<< counter <<'\n'; lock.unlock();std::this_thread::sleep_for(std::chrono::seconds(1));}}; std::thread increment_foo(increment, std::ref(foo_count), std::ref(foo_count_mutex), "foo");std::thread increment_bar(increment, std::ref(bar_count), std::ref(bar_count_mutex), "bar"); std::thread update_overall([&](){ done_mutex.lock();while(!done){ done_mutex.unlock();int result = std::try_lock(foo_count_mutex, bar_count_mutex);if(result ==-1){ overall_count += foo_count + bar_count; foo_count =0; bar_count =0;std::cout<<"overall: "<< overall_count <<'\n'; foo_count_mutex.unlock(); bar_count_mutex.unlock();}std::this_thread::sleep_for(std::chrono::seconds(2)); done_mutex.lock();} done_mutex.unlock();}); increment_foo.join(); increment_bar.join(); done_mutex.lock(); done =true; done_mutex.unlock(); update_overall.join(); std::cout<<"Done processing\n"<<"foo: "<< foo_count <<'\n'<<"bar: "<< bar_count <<'\n'<<"overall: "<< overall_count <<'\n';}
Possible output:
bar: 1 foo: 1 foo: 2 bar: 2 foo: 3 overall: 5 bar: 1 foo: 1 bar: 2 foo: 2 bar: 3 overall: 10 bar: 1 foo: 1 bar: 2 foo: 2 overall: 14 bar: 1 foo: 1 bar: 2 overall: 17 foo: 1 bar: 1 foo: 2 overall: 20 Done processing foo: 0 bar: 0 overall: 20
[edit]See also
(C++11) | locks specified mutexes, blocks if any are unavailable (function template) |
